Radiation detection systems generally employ a radiation detector such as a germanium or scintillation detector or photodiode to detect radiation from a radiation source such as alpha or gamma rays or light. The detection of such energy results in a charge pulse whose amplitude is proportional to the energy of the incident radiation. The charge pulse is converted to a voltage pulse by a feedback capacitor incorporated in a preamplifier. A resistor is added in parallel with the capacitor in order to discharge the capacitor in preparation for the next pulse in a reasonable amount of time to allow for processing of successive pulses. The parallel combination of the capacitor and the resistor defines the time constant of the exponentially decay of the voltage pulse. The voltage pulse with the exponentially decaying trailing edge is submitted to an RC filter to shorten the pulse and improve the signal-to-noise ratio. However, this filter when supplied with an exponentially decaying signal produces a filtered signal with an undesirable undershoot, i.e., an excursion below baseline voltage. This is a serious problem since the radiation pulses arrive randomly in time and succeeding pulses can occur during the undershoot of a previous pulse in that case, the measurement of the amplitude of the succeeding pulse would be distorted. To compensate for this a pole-zero cancellation circuit has been used to eliminate the undershoot. In this scheme a portion of the voltage pulse input to the RC filter is diverted around the filter and combined with the filter output to cancel the undershoot. This was originally done manually. (See Nowlin et al., "Elimination of Undesirable Undershoot in the Operation and Testing of Nuclear Pulse Amplifiers", Rev. Sci. Instr., Instr., vol. 36, No. 2 , December 1965, pp 830-839.) However, here was much difficulty encountered in having untrained non-technical personnel such as at medical clinics compelled to adjust the shunting resistance or other component to null the undershoot and avoid overshoot. To meet this problem a more automatic approach was proposed as in U.S. Pat. No. 4,866,400, fully incorporated herein by reference. However, even with this improved approach, more accuracy is desirable. For example, elimination of errors (glitches, pedestals, offsets and temperature drift) in the analog automatic auto-PZ sampling circuit.